Pope Francis is once again making history. He met in Havana today with the leader of the Russian Orthodox Church. Patriarch Kirill of Moscow was himself on an official visit to Cuba. Not since the establishment of the Russian church more than 400 years ago has a Russian patriarch met with the Pope. Afterward, the two men exchanged gifts and, with Cuban President Raul Castro standing off to one side, Patriarch Kirill said the two churches would continue to work together. Pope Francis followed him.

POPE FRANCIS: (Through interpreter) We spoke as brothers. We have the same baptism. We are bishops. We spoke of our churches. We believe that unity is done in the walk of life.

SHAPIRO: NPR's Tom Gjelten is here in the studio to talk about this historic meeting of religious leaders. Hi, Tom.

TOM GJELTEN, BYLINE: Hi, Ari.

SHAPIRO: What exactly is and is not historic about this event?

GJELTEN: That's an important question, Ari, because, you know, lately we've heard a lot about this so-called great schism between Eastern and Western Christianity that happened nearly a thousand years ago. At that time, then Pope Leo IX excommunicated the patriarch of Constantinople, which, at the time, was the center of the eastern or Greek Christian Church. And then the patriarch turned around and excommunicated the pope from his church. That was the culmination of some big disagreements over both practical and theological issues from whether priests could marry to the understanding of the Holy Trinity, so that was the big breakup.

But that mutual excommunication was undone more than 50 years ago when Pope Paul VI met with the then patriarch of Constantinople. That was a momentous meeting. And there've been other meetings since then. So this one in Havana today was not the first in a thousand years between a pope and a patriarch as some reports would suggest. It is the first between a pope and a Russian patriarch, and that is important because the Russian church is by far the biggest in the Orthodox world. And the Russians have been reluctant to endorse this larger Catholic Orthodox dialogue that's been underway for 50 years.

SHAPIRO: Given that reluctance, why is this meeting happening at all? Why now?

GJELTEN: I think the biggest factor is the persecution of Christians in the Middle East, most of whom are Orthodox Christians. So the Russian patriarch and Pope Francis have a mutual interest in supporting those Christians who are literally on the run from that ISIS onslaught. On the Russian side, another factor is that President Putin has been on a charm offensive lately with the West. The Russian church is a strong political ally of the Kremlin, so it's not surprising the patriarch would follow Putin's lead. Finally, credit has to go to Francis himself, you know? He's a big promoter of dialogue and reconciliation.

SHAPIRO: Likely talking about the crisis in the Middle East, Christians in the crosshairs - what else do we think they're likely discussing?

GJELTEN: The pope - they signed a declaration afterwards. The pope described it as a series of initiatives. Patriarch Kirill said they'd agreed to work together for the future of Christianity and civilization itself against war. It's not clear they bridged the issues that still divide them. The patriarch just said the meeting have them an opportunity to understand the positions of each other.

SHAPIRO: But still some divisions between them.

GJELTEN: The biggest is the authority of the pope. The Orthodox Christians don't even call him the pope. They just see him as the bishop of Rome and say he doesn't have any authority over them. Another one is communion - Orthodox Christians and Catholic Christians can't take communion in each others' churches.

SHAPIRO: And Pope Francis goes from Havana to Mexico. What happens there?

GJELTEN: Well, that was actually the whole point of the trip. I mean, the Cuba stop was added at the last minute. The pope, as you know, has this big interest in meeting with the most extreme, the marginalized of the population. He's going up to the border where there's a lot of violence. He's going to the South where there's a lot of poverty.